Spiked rods of uric acid crystals from synovial fluid photographed under a microscope with polarized light. In patients with gout, such crystals can accumulate in the joints, causing pain and inflammation.

A fruit fly’s compound eye contains 800 prism-like facets whose six distinct photoreceptor cells capture light coming in from different angles in space. These signals must all find their way to different spots in the fly brain’s visual map of the world.